The present invention relates to films that are receptive to solvent-based inkjet inks and methods of printing onto such films. More specifically, the present invention relates to extruded films that are receptive to solvent-based inkjet inks and methods of printing onto such films. A variety of polymeric sheets may be prepared including various sheeting for signage and commercial graphic films for advertising and promotional displays.
A variety of print methods have been employed for imaging various sheet materials. Commonly employed print methods include gravure, off-set, flexographic, lithographic, electrographic, electrophotographic (including laser printing and xerography), ion deposition (also referred to as electron beam imaging (EBI)), magnetographics, inkjet printing, screen printing, and thermal mass transfer. More detailed information concerning such methods is available in standard printing textbooks.
One of ordinary skill in the art appreciates the differences in these various print methods and recognizes that a combination of ink and receiving substrate that results in high image quality in one printing method often exhibits an entirely different image quality with another print method. For example, in contact printing methods such as screen printing, a blade forces the ink to advance and wet the receiving substrate. Image defects are typically due to a subsequent recession of the ink contact angle with the substrate. In the case of non-contact printing methods, such as inkjet printing, the individual ink drops are merely deposited on the surface. In order to achieve good image quality, the ink drops need to spread, join together, and form a substantially uniform, leveled film. This process requires a low advancing contact angle between the ink and the substrate. For any given ink/substrate combination, the advancing contact angle is typically significantly greater than the receding contact angle. Accordingly, ink/substrate combinations that result in good image quality when printed with contact methods such as screen printing, often exhibit insufficient wetting when imaged with non-contact printing methods such as inkjet printing. Insufficient wetting results in low radial diffusion of the individual ink drops on the surface of the substrate (also referred to as xe2x80x9cdot gainxe2x80x9d), low color density, and banding effects (e.g., gaps between rows of drops).
Another important difference between screen printing and inkjet printing is the physical properties of the ink. Screen printing ink compositions typically contain over 40% solids and have a viscosity of at least two orders of magnitude greater than the viscosity of inkjet printing inks. It is not generally feasible to dilute a screen printing ink to make it suitable for inkjet printing. The addition of large amounts of low viscosity diluents drastically deteriorates the ink performance and properties, particularly the durability. Further, the polymers employed in screen printing inks are typically high in molecular weight and exhibit significant elasticity. In contrast, inkjet ink compositions are typically Newtonian.
Inkjet printing is emerging as the digital printing method of choice due to its good resolution, flexibility, high speed, and affordability. Inkjet printers operate by ejecting, onto a receiving substrate, controlled patterns of closely spaced ink droplets. By selectively regulating the pattern of ink droplets, inkjet printers can produce a wide variety of printed features, including text, graphics, holograms, and the like. The inks most commonly used in inkjet printers are water-based or solvent-based. Water-based inks require porous substrates or substrates with special coatings that absorb water.
In one aspect, the invention provides an image receptor medium comprising an extruded image receptive layer that is receptive to solvent-based inkjet ink. The image receptive layer comprises a blend of a) a carrier resin comprising modified polyolefin or poly urethane resin, or combinations thereof and b) an ink absorptive resin compatible with said carrier resin and present in an effective amount and having a Hildebrand Solubility Parameter of said absorptive additive within about 3.1 (MPa)1/2 of the solvent of the ink, wherein the image receptive layer has an ink solvent absorption of at least 50% greater than a film of carrier resin alone.
In another aspect, the invention provides a method of printing with an inkjet printer comprising the step of jetting a solvent-based inkjet ink onto an image receptor medium comprising an extruded image receptive layer that is receptive to solvent-based inkjet ink, said image receptive layer comprising a blend of a) carrier resin; and b) an effective amount of ink absorptive resin compatible with said resin and having a Hildebrand Solubility Parameter of said absorptive additive is within about 3.1 (MPa)1/2 of the solvent of the ink and wherein the image receptive layer has an ink solvent absorption of at least 50% greater than a film of carrier resin alone.
In another aspect, the invention provides a method of making a multi-layer image receptor medium comprising the step of: coextruding an image receptive layer with a core layer, wherein the image receptive layer comprises a blend of a) carrier resin comprising modified olefin, urethane, or acrylic resin or combinations thereof; and b) an effective amount of ink absorptive resin compatible with said resin and having a Hildebrand Solubility Parameter of said absorptive additive is within about 3.1 (MPa)1/2 of the solvent of the ink and wherein the image receptive layer has an ink solvent absorption of at least 50% greater than a film of carrier resin alone.
In yet another aspect, the invention provides an imaged ink receptor media comprising an image receptive layer of the invention having an image printed thereon.
The articles of the invention are useful as an intermediate or as a finished product for signage and commercial graphic films.